This invention relates to an improved process for flocculating suspensions of solids. More particularly, this invention relates to such a process wherein the flocculant employed is an anionic copolymer comprising comonomers of 2-acrylamido-2-methylpropanesulfonic acid and acrylamide.
Flocculants are reagents which are added to suspensions of solids to cause the solids to floc and settle. A highly effective type of flocculant is the polymeric type since this type can be prepared in numerous variations. Typically, polymeric flocculants are of three types, nonionic, cationic, and anionic. The particular type of flocculant to be used in a given application will generally depend upon the nature of the surface of the suspended solids.
To provide nonionic polymers, nonionic monomers such as acrylamide are polymerized under conditions which lead to a nonionic polymer. Polymers containing amine groups, primary, secondary, tertiary, and quaternary types provide typical cationic flocculants with increased charge increasing in the order given. For anionic polymers, carboxylic acid groups are introduced into the polymer. Polymers containing sulfonic acid groups were also introduced as anionic flocculants.
Water-soluble sulfonate polymers have, however, been known in the art as effective flocculants. U.S. Pat. No. 3,692,673 to Hoke teaches the use of polymers of acrylamido sulfonic acids and their salts as useful flocculants for aqueous systems, especially in combination with inorganic flocculants. Similarly, U.S. Pat. No. 3,617,572 to Monagle teaches the use of copolymers of acrylamide and an alkali metal salt of vinyl sulfonic acid as effective flocculants. Despite these teachings, there continues to exist the need for improved processes for flocculating solid suspensions. The provision for such processes would constitute yet another significant advance in the art.